The nucleus of the solitary tract (NTS) is the brain region most implicated in chemoreflex-induced blood pressure elevation and hypertension-evoked resetting of baroreceptor reflexes, both of which can be modulated through activation of local angiotensin-1 (AT1) receptors. Project 2 will test the central hypothesis that AT1 receptors in the NTS have subcellular distributions supporting direct involvement in cherno- and/or barosensory reflexes and interactions with both catecholamines and NAD(P)H oxidase, an enzyme implicated in the acute and long-term effects of angiotensin II (Angll). This will be achieved by using (1) high resolution electron microscopic immunocytochemical dual labeling of the relevant receptors and NAD(P)H oxidase subunits, and (2) both ultrastructural analysis and patch-clamp recording in barosensory neurons identified by anterograde transport of DiA in rat NTS. There are 5 Specific Aims. Aims 1 and 2 will test the hypothesis that AT1 and alpha2-adrenergic receptors are co-localized within presynaptic axons or their dendritic targets in the NTS, where their distributions are consistent with opposing actions of their agonists on chemo- or barosensory neurons. Aim 3 will test the hypothesis that the physiological actions of Ang II in NTS barosensory neurons are mediated through opening of voltage-dependent Ca 2+ channels also affected by reactive oxygen species (ROS) generated by NAD(P)H oxidase, whose subunits are present in many of the cells that contain AT1 receptors. The opening of voltage-gated Ca 2+ channels is essential for activation of NMDA and certain types of AMPA receptors that are the major mediators of chemosensory and barosensory transmission, respectively. These receptors, like NAD(P)H oxidase, are composed of multiple subunits showing activity-dependent mobilization to plasma and cytoplasmic membranes. Changes in the subcellular distribution of immunogold labeling for glutamate (Aim 4) or NAD(P)H oxidase (Aim 5) subunits will be used to study the potential role of this plasticity in the blood pressure elevations produced either by chronic intermittent hypoxia in the rat model of sleep apnea, or Angll-induced hypertension. Together, the results will contribute to understanding the brain mechanisms underlying the development and maintenance of hypertension.